In 3GPP (3rd Generation Partnership Project), the W-CDMA system has been standardized as the third-generation cellular mobile communication system, and the services have been started successively. ESDPA with the communication speed further increased has been also standardized, and the service has been started.
On the other hand, in 3GPP, the evolution of third-generation radio accessing (Evolved Universal Terrestrial Radio Access: represented hereinbelow as “SUTRA”) has been studied.
As the downlink of EUTRA, OFDM (Orthogonal Frequency Division Multiplexing) system has been proposed. As the uplink of EUTRA, single-carrier communications scheme of DFT (Discrete Fourier Transform)-spread OFDM system has been proposed.
FIG. 14 shows the outline of the downlink and uplink in EUTRA. Mobile station apparatuses (MS) are connected to a base station apparatus (BS).
The downlink for EUTRA is configured of a downlink pilot channel DPiCH (Downlink Pilot Channel), a downlink synchronization channel DSCH (Downlink Synchronization Channel), a downlink shared channel PDSCH (Physical Downlink Shared Channel), a downlink control channel PDCCH (Physical Downlink Control Channel) and a common control channel CCPCH (Common Control Physical Channel).
The uplink for EUTRA is configured of an uplink pilot channel UPiCH (Uplink Pilot Channel), a random access channel RACH (Random Access Channel), an uplink shared channel PUSCH (Physical Uplink Shared Channel) and an uplink control channel PUCCH (Physical Uplink Control Channel) (see non-patented documents 1 and 2, for example).
Here, the random access channel (RACH) for the uplink of EUTRA uses a bandwidth of 1.25 MHz, and a plurality of access channels are provided so as to deal with accesses from a large number of mobile station apparatuses. FIG. 15 shows one example of the random access channel (RACH).
In FIG. 15, the horizontal axis represents time and the vertical axis represents frequency. FIG. 15 shows the configuration of one radio frame. This radio frame is split into a plurality of radio resources. In this example, the radio resources are constructed of units each of which has a domain having 1.25 MHz in frequency direction and 1 ms in time direction. Random access channels (RACH) and uplink shared channels PUSCH described in FIG. 15 are allotted to these regions as shown in the drawing.
In this way, the minimum unit of the random access channel (RACH) uses a bandwidth of 1.25 MHz. Here, in FIG. 15, the uplink pilot channels UPiCH are distributed in symbol units or in sub-carrier units within the uplink shared channel PUSCH region. Further, since in EUTRA a plurality of channels are prepared for the random access channel (RACH), it is possible to deal with a plurality of random accesses at the same time.
Here, the minimum unit of the random access channel (RACH) uses a bandwidth of 1.25 MHz, and one random access channel (RACH) is prepared in one sub frame on the frequency axis and a plurality of random access channels (RACH) are prepared in one frame depending on the frequency bandwidth of the base station apparatus, whereby it is possible to deal with access from many mobile station apparatuses (see non-patented documents 3 and 4, for example).
Now, FIG. 16 shows a configurational example of random access channels depending on the bandwidth in the base station apparatuses. FIG. 16 is a diagram in which the horizontal axis represents time and sub-frame numbers 0 to 9 are assigned in each frame.
Here, when the bandwidth in the base station apparatus is 1.25 MHz, one random access channel (RACH) is assigned to every two frames (FIG. 16(a)). Similarly, when the bandwidth in the base station apparatus is 5 MHz, one channel is assigned to every frame (FIG. 16(b)). When the bandwidth in the base station apparatus is 10 MHz, two channels are assigned to every frame (FIG. 16(c)). When the bandwidth in the base station apparatus is 15 MHz, three channels are assigned to every frame (FIG. 16(d)). When the bandwidth in the base station apparatus is 20 MHz, five channels are assigned to every frame (FIG. 16(e)).
The purpose for using the random access channel (RACH) is mainly to establish synchronization in the uplink between the mobile station apparatus and the base station apparatus, and also expected to transmit a few bits of information such as for a scheduling request for allocating radio resources to shorten connection time.
Here, in random access, there is two accessing methods, Contention based Random Access and Non-contention based Random Access. The Contention based Random Access is a random access that may cause collision between mobile station apparatuses, and is a normal random access. On the other hand, the Non-contention based Random Access is a random access that will never cause collision between mobile station apparatuses, and is a random access used for fast synchronization between a mobile station apparatus and a base station apparatus and is executed for a special case such as handover etc. under the initiative of the base station apparatus.
In the case of random access, only the preamble is transmitted for synchronizing. The preamble includes a signature which is a signal pattern representing information. Some tens of kinds of signatures are prepared so as to be able to express some bits of information. At present, it is presumed that 6 bit information is transmitted, hence it is presumed that 64 kinds of signatures are prepared.
It is presumed that of 6 bits of information, 5 bits are assigned to the random ID and the remaining one bit is assigned to the downlink pathloss/CQI (Channel Quality Indicator) or the like.
Here, the communication procedures of the Contention based Random Access and the Non-Contention based Random Access will be roughly described.
To being with, FIG. 17 shows the sequence example of the Contention based Random Access.
First, the mobile station apparatus selects a signature based on the random ID, the downlink path loss/CQI information or the like and transmits a random access preamble through the random access channel (RACH) (message 1).
When receiving the preamble from the mobile station apparatus, the base station apparatus calculates the gap of in timing of synchronization between the mobile station apparatus and the base station apparatus from the preamble, performs scheduling for transmitting a L2/L3(Layer2/Layer3) message, assigns a Temporary C-RNTI (Cell-Radio Network Temporary Identity), sets a RA-RNTI (Random Access-Radio Network Temporary Identity) that represents a response to the mobile station apparatus that transmitted the random access preamble to the random access channel (RACH), to the downlink control channel (PDCCH), and transmits a random access response including the synchronization timing gap information, scheduling information, Tempolary C-RNTI and the signature ID number (or random ID) of the received preamble, to the downlink shared data channel (PDSCH) (message 2).
When confirming that a RA-RNTI exists in the downlink control channel (PDCCH), the mobile station apparatus checks the content of the random access response set in the downlink shared data channel (PDSCH) to extract the response including the signature ID number (or random ID) of the transmitted preamble.
Then, the mobile station apparatus corrects the synchronization lag and transmits L2/L3 message at least including a C-RNTI (or Temporary C-RNTI) through the scheduled radio resource (message 3).
Here, if the mobile station apparatus has kept waiting the random access response from the base station apparatus for a certain period of time but does not receive the random access response including the signature ID number of the transmitted preamble, the apparatus transmits the random access preamble once again.
When receiving the L2/L3 message from the mobile station apparatus, the base station apparatus transmits to the mobile station apparatus a contention resolution for determining whether there is a collision occurring between mobile station apparatuses, using the C-RNTI (or Tempolary C-RNTI) included in the received L2/L3 message (message 4). When the mobile station apparatus receives the contention resolution, synchronization between the mobile station apparatus and the base station apparatus is established.
Subsequently, the sequence example of the Non-contention based Random Access will be described with reference to FIG. 18.
First, the base station apparatus selects a signature, and transmits random access preamble allocation to the mobile station apparatus (message 1). The mobile station apparatus, using the given signature, transmits a random access preamble through the random access channel (RACH) (message 2).
When receiving the preamble from the mobile station apparatus, the base station apparatus calculates the synchronization time lag between the mobile station apparatus and the base station apparatus from the preamble, sets a RA-RNTI or C-RNTI that represents a response to the mobile station apparatus that transmitted the random access preamble to the random access channel (RACH), to the downlink control channel (PDSCH), and transmits a random access response including the synchronization time lag information (message 3). The mobile station apparatus corrects the synchronization time lag based on the received random access response. Thereby, synchronization between the mobile station apparatus and the base station apparatus is established.
Here, the signature used for Contention based Random Access and the signature used for Non-contention based Random Access are different.
Referring next to FIG. 19, the sequence at the time of handover of mobile station apparatus will be described taking an example in which the random access procedures are of Non-contention based Random Access.
At the preparation stage of handover, the mobile station apparatus measures the conditions of the radio waves on neighboring base station apparatuses and transmits the measurement report to the currently accessing base station apparatus or the handover originating base station apparatus. The handover originating base station apparatus, referring to the measurement report from the mobile station apparatus, selects the best-qualified handover target base station apparatus. Then, the base station apparatus transmits a handover request message to the selected handover target base station apparatus.
When receiving the handover request message from the handover originating base station apparatus, the handover target base station apparatus assigns a C-RNTI and a signature ID number to be used at the handover target base station apparatus to the mobile station apparatus to be handed over and transmits a handover request acknowledgement message including the C-RNTI and signature ID number as a response to the handover request, to the handover originating base station apparatus. The handover target base station also calculates the end time of the duration available for the signature corresponding to the signature ID and transmits the calculation included in the handover request acknowledgement message.
The handover originating base station apparatus extracts the C-RNTI, signature number and end time included in the handover request acknowledgement message, and transmits a handover command message included with the extracted C-RNTI, signature number and end time, to the mobile station apparatus (message 1).
When receiving the handover command message, the mobile station apparatus takes downlink synchronization with the handover target base station apparatus and checks the position of the random access channel (RACH) from the broadcast channel. The mobile station apparatus uses the signature given by the handover command message and transmits a random access preamble to the handover target base station apparatus through the random access channel (RACH) (message 2).
When detecting the signature from the random access channel (RACH), the handover target base station apparatus calculates the synchronization time lag to perform uplink scheduling for transmitting a handover complete message from the mobile station apparatus and transmits a random access response message including the synchronization information, scheduling information and signature ID number (message 3).
When receiving the random access response including the transmitted signature ID number, the mobile station apparatus corrects the synchronization timing lag from the synchronization information and transmits a handover complete message through the scheduled radio resource.
However, if no selectable signature has been left at the base station apparatus, there is a possibility of collision occurring, hence random access by Contention based Random Access may be used in some cases even through longer time is consumed for the random access procedures.    Non-patented document 1: 3GPP TS (Technical Specification)36.211, V1.10(2007-05), Technical Specification Group Radio Access Network, Physical Channel and Modulation (Release 8)    Non-patented document 2: 3GPP TS (Technical Specification)36.212, V1.20(2007-05), Technical Specification Group Radio Access Network, Multiplexing and channel coding (Release 8)    Non-patented document 3: R1-073436, Texas Instruments, “Random Access slot Configurations”, 3GPP TSG RAN WG1 Meeting #50, Athens, Greece, 20-24 Aug., 2007    Non-patented document 4: 3GPP TS (Technical Specification) 36.300, V8.10(2007-06), Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access Network (E-UTRAN), Overall description Stage 2